Flog (or beat) a dead horse

: Where does the phrase
: "beat a dead horse" come from
: I understand the meaning, but looking for the origin.

BEAT (OR FLOG) A DEAD HORSE - "Though he supported the measure, British politician and orator John Bright thought the Reform Bill of 1867, which called for more democratic representation, would never be passed by Parliament. Trying to rouse Parliament from its apathy on the issue, he said in a speech, would be like trying to 'flog a dead horse' to make it pull a load. This is the first recorded use of the expression, which is still common for 'trying to revive interest in an apparently hopeless issue.'." From the "Encyclopedia of Word and Phrase Origins" by Robert Hendrickson (Fact on File, New York, 1997)